Frequency generating system



Jan. 25, 1949. M. A. LALANDE FREQUENCY GENERATING SYSTEM Filed July 25, 1947 M %6 f F. f mm /m m 7 7 w w m m x n rw: Z M m m m w c v F 12x5 n WF S.

IN VEN TOR. MARC ,4. lflLfl/VDE A T TOR/VF) Patented Jan. 25, 1949 UNITED STATES FREQUENCY GENERATING SYSTEM Marc Andre Lalandc, Paris, France, assignor to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application July 25, 1947, Serial No. 763,619 In France February 15, 1946 Section 1, Public Law 690, August 8, 1946 The invention relates to frequency generator systems and particularly to such systems which generate sub-harmonic frequencies of a base frequency. V

objectof the invention is to provide a systemfor generating sub-harmonics of a base freuency 'wherein said sub-harmonics are exact sub-multiples of the base frequency.

Another object of the invention is to provide a system for generating exact sub-multiple harmonic frequencies of a base frequency which varies over a predetermined range of frequency.

It is often required, for example in telephone carrier systems, to provide a series of frequencies which are exact multiples of a base frequency and which are vary stable. Since the base frequency of such systems must be a low frequency inprder thatits harmonics shall be in the desired frequency range, an oscillator of such a low frequency" must be provided. Such oscillators of such low frequencies are not susceptible of great stability and a resulting instability of all the harmonics of such an oscillator results.

According t'o'theinvention the series of barmonically related frequencies is provided by a system for generating sub-harmonic frequencies of a-base frequency. Thus, the base frequency "oscillator may be an oscillator of higher frequency than any other frequency of the series and may be for example, a crystal oscillator of say 100 k. c. which provides a system of harmonically related frequencies which is known to be more stable than previous systems based on an oscillator of lower frequency.

Other objects and advantages of the invention ,will appearin the followin detailed description and claims andiri the drawings, in which q .Fig., 1. hows. a .block diagram illustrating the prihciplesof the invention;

Fig. 2: shows the schematic diagram of a first embodiment of .the invention; and

Fig. 3 shows a schematic diagram of a second embodiment of the invention.

. Referring to Fig. 1, a source I of frequency F- 'mf where F is called the base frequency, m is any integer, and f is a sub- -harmonic frequency is shown connected to a frequency changer:

9 Claims. (Cl. 250-36) 2. This frequency f is fed from amplifier 3 to a harmonic generating circuit i which multiplies frequency f by a factor mi so that frequency f1:=(m1). appears at the output of harmonic generator 4. Part of this output is connected to a selective amplifier 5 and thence to changer2 as mentioned above, the remainder of this output constituting a frequency 1 Which is an mth degree sub-multiple of the base frequency F.

In order to determine the stability of this system, suppose that, at a given instant the frequency supplied to frequency generator 4' is f+Af whereAf is a deviation from the desired frequency I. Then f1 is changed to a new value f1 such that Then the output frequency of frequency changer 2 will be The deviation in frequency A is thus multiplied by a factor (m1) and subtracted from frequency f resulting in a very rapid correction of the orig inal assumed incorrect frequency ,f-l-Af so that the correct frequency ,f quickly is reestablished.

The loop comprising changer 2, amplifier 3, frequency multiplier 4, and amplifier 5 must possess a net gain to maintain sustained oscillations; this loop having no particular frequency, the various filtering of selective means can be constructed so as to have a certain band Width which may'at- 'tain a value equal to one-half the frequency ,f. It follows therefore that the only frequency controlling the system is the base frequency F. Thus the system described by the invention provides a greater frequency stability than previous systems.

The system described above presupposes eiistence of a steady state oscillation and it is necessary to provide an adequate device to start oscillations in the loop when it is to be used as a part of a system for carrier telephony. This can be done in several Ways such as the injection of either frequency f or ii by means of a temporarily operative oscillator or by shock exciting one of the selective amplifiers.

Referring to Fig. 2 a circuit is shown for a particular loop which is rendered operative by tem porary self-oscillation of an amplifier in the loop.

A base frequency oscillator comprising a crystal controlled oscillator utilizing a triodesection of electron tube I, and a crystal Z'ground to oscillate at the' base frequency F produces stable oscillati'ons'at a frequency F=mf. The other elements tubes and 6 which are resistance coupled in the conventional manner, and a coupling trans former l the primary winding of which is' in "the anode circuit of tube 5. of transformer i is connected to a band pass filter of conventional type designed to pass a band of frequency on either side of the frequency ,f =F f 1. the tuned secondary winding of transformer l and the series capacitaiocednductance resonant circuit 8. This band-pass filter may be designed to pass" any particular frequency band desired for particular requirements of stability.

1 The frequency ).=Ff1, afterpassing through the band-pass filter, is impressed on a full-wave rectifier system 9. The action of the band-pass filter and the'full-wave rectifier 9 is to generate ah'armo'nic of frequency f and this harmonic may, by adjustment of these circuit elements be made the (m-l) harmonic of 1. Thus a liarmonicfrequency (m1)f is impressed across a transformer Hi as well as appearing at terminals 1 I' for use, for example, in a carriertelephone system. y

The full wave rectified current output of rectifier 9 is impressed on a'relay 12 operating contacts i3 insuch away that when a frequency f is rectified by rectifier 9, relay it opens contacts l3 disconnecting a feedback circuit including resistance M and capacitance 15' which is connected between thecontrol grid of amplifier tube 5 and the anode of amplifier tube 5 to provide a feedback circuit between tubes 5 and 6, whereby these tubes shall temporarily oscillate at a frequency f=F-f1as determined by-the tuned transformers 4 and I when contacts 13 are-engaged, namely where no frequency f-appears in the secondary winding of transformer I.

:Transforrner *ID' is connected to a band-pass filter f6 adjusted to possess a centerv pass frequency of f1=(m-l)f. An amplifier l'l possessing a tuned output transformer 18 amplifies -and further adjusts the band-pass characteristic of filter i6 and impresses the frequency f1 on a control grid of the frequency changer portion of tube l by connector 3 as described above. 'If the tifier 22 and terminals 23. The'b'and pass filter issimilar tothat of Fig. 2 and its bandwidth may be adjusted as therein described.-

. The combination of the filter 2i and. rectifier .--22 -"produces the (wt-+1) harmonic. of the frequency if and-this frequency. (ma-.1) f. appears at terminals 23-for use in completing the ring The secondary Winding? This band-pass filter is composed of circuit as in Fig. 2 and for use in, for example, a carrier telephone system.

The shock excitation is applied amplifier tube I as follows: As long as frequency appears across rectifier .22, relay 24, connected to the output of the rectifier; "is activated andhold's'its contacts 25 open allowing the amplifier to proceed normal- 1y; however, when the rectifier 22 is not supplied with a sufiicient magnitude of voltage of fre- 'quenc f, "-r'elay-24 is deactivated and allows its contacts 25 to close, as shown in Fig. 3. A cirpuit isv completed from ground through contacts "25,'bacl-f'ccntacts "25 of relay 21, coil of relay 21,

a resistance 28 to high tension. This circuit activates relay 21, closing its front contacts 29 "which instantly cuts the voltage at point 30 to I zero. This instantaneous change in voltage at point 35 causes a transient surge in amplifier tube It andits associated circuits whereby a frequency f is generated because ithe amplifier is tuned as discussed in connection with Fig. When relay 2'!- is so activated, its back contact 26 opens -caus- .ing a deactivation of relayZ]. As long S contacts 23 are closed, relay 2'! will thus alt ately be activated and deactivated accorcling itoi-jits' natural. period, continually shocking tl ie ampli fier circuit with surges of volta'ge-untila su-fiicient voltage of frequency f appears-across relay 24 to open contacts 25 by activating relay' 2}. I

The rest of the operation is as in 2 where frequency (m1)f appearing at terminals Sis fd to a band pass fil-te r' and amplifier and; thence back to a frequency changer-also supplied with a base frequency F whereby a frequency is supplied to'th'e amplifier.

Although particular circuits have been utilized to illustrate the principles of the. invention-it is clear that other circuits could bedesignedaccording to'these principles without exceedingthe spirit and scope of the invention.

I claim: p

1. An arrangement'for obtaining multiple subharmonic frequency energy from a'stable source of basefrequency energy comprising asource' 'of modulation frequency energy, means for modulatingsaid base frequency 'energy with said modulation frequency en'ergy 'to' obtain 'a subharmonic frequency energy; a rulrwaveeeedfier, a sub-harmonic frequency ampIifiercISnditiOr-iii for operating in an' oscillatory ora nonf 'os cillatory state, and means for applyingsai ubharmonic frequency energy throughfs ajid amplifier 'to said full wave rectifier, means responsive to the output of said amplifier for contro ng the state of operation of aid-1 subfrequency'" amplifier, saidsou'rce of r'n'odiila n -frequency energy comprising" meansgbrf deriviii g' fromsaid' rectifier output ;said 'rnodulation'freque ncy energy and means for derivingfrorri said rtifir Output the multiple Sub h8lfm6fli(frequency energy. I I

2.Anj arrangement acc rdin e01 claim -l, wherein' 's'aid means for conditioning' sa1d subharmonic frequency amplifier fddl'lipflss fhans responsive tofthe amplitude ofth'e' output of said rectifier for stopping 'or starting oscillations in saida'mplifier. I I f 3. An arrangement. according to claim 1, w r n. d an or eediti ihf pr}os tion; of said amplifier compr ises means sponsive idhe .eu t a e ifi to can ncamplifier to oscillate in response to therectiiled sub-harmonic frequency energy falling below a given level and causes said amplifier to stop oscillating when said rectified sub-harmonic frequency energy rises above said given level.

4. An arrangement according to claim 1, wherein said amplifier comprises a circuit tuned to said sub-harmonic frequency and said means for conditioning said amplifier, comprises means for shock exciting said tuned circuit.

5. An arrangement according to claim 5, wherein said circuit is shock excited in response to the rectified sub-harmonic frequency energy falling below a certain level and said circuit is maintained non-oscillatory when the rectified sub-harmonic frequency energy is above said given level.

6. An arrangement according to claim 1, wherein said means for modulating said base frequency energy with said modulation frequency energy to obtain said sub-harmonic frequency energy comprises a selective circuit tuned to said sub-harmonic frequency.

7. An arrangement according to claim 1, wherein the output of said amplifier is passed through a band pass filter having a pass band 25 6 above or below said sub-harmonic frequency before application to said full wave rectifier.

8. An arrangement according to claim 1, wherein said means for conditioning for oscillation of said amplifier comprises a relay coupled MARC ANDRE LALANDE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,039,657 Osborne May 5, 1936 2,124,191 Geiger July 19, 1938 2,334,678 Crosby. Mar. 21, 1944 

